1. Field of the Invention
The present invention relates generally to mobile stations operating in a wireless communication network, and more particularly to methods and apparatus for expeditiously releasing network resources for a mobile station based on low battery and lost signal conditions.
2. Description of the Related Art
A wireless communication device, such as a mobile station operating in a wireless communication network, may provide for both voice telephony and data communications (e.g. IP packet data communications) for an end user. A mobile station may, for example, be compatible with 3rd Generation (3G) communication standards (such as IS-2000 Release 0) and utilize Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA) wireless network technologies.
Many mobile stations receive power from one or more batteries or battery packs which are connected to the mobile stations. In current CDMA-based wireless networks, at least some service providers require that a mobile station automatically power itself off before its battery charge reaches an “empty” condition. When a low battery condition is detected, the mobile station performs a power down procedure which is similar to the process that occurs when the mobile station is manually powered off by the end user. If the mobile station is in an “idle” state, the power down procedure includes generating an audible alert, sending a power down registration to the network on an access channel, and powering itself off. If the mobile station is in a “dormant” packet data session, the mobile station is required to setup a data call merely to tear down a Point-to-Point (PPP) session established with the network, terminates the call, send the power down registration, and power itself off. If the mobile station is in an “active” traffic channel call, the mobile station sends a release order message with power down registration on the traffic channel and powers itself off. Some alternative methods are also possible and in general, these methods may be referred to as conventional power down registration techniques.
The purpose of sending the power down registration before the mobile station powers itself down is to conserve network resources. After the receipt of the power down registration, the wireless network “knows” that the mobile station is unavailable and no longer requires service from the network. The wireless network knows, for example, that it is futile to page the mobile station for incoming calls when it is unavailable. In addition, the wireless network may release network resources such as an IP address and memory assigned to the mobile station when the mobile station is unavailable. This includes, for example, a Radio Access Network (RAN)-Packet Data Service Node (PDSN) binding or a Foreign Agent and Home Agent binding in a cdma2000™ network.
When the mobile station is in an “active” traffic channel call, which may be a voice, data, or other type of call, it is not always possible for the mobile station to adequately transmit a release order message with power down registration before an actual hardware power failure occurs due to the magnitude of the battery's voltage fluctuation. Given wide current fluctuations, the mobile's battery voltage may drop across both soft and hard “power-off” thresholds at nearly the same time and cause the transmitted signal to be lost. When the mobile station's battery condition becomes poor in an idle state or a dormant data packet session, the mobile station may also experience a hardware power failure before it completes the power down procedure due to access probe or traffic channel transmission activity.
The result may appear to the wireless network as a “call drop” due to reverse link fading. When this occurs, the wireless network does not expeditiously release network resources for the mobile station. Over a subsequent time period during which the mobile station is inoperable and unavailable, the wireless network continues to page the unreachable mobile station for incoming communications and fails to deassign and reallocate its previously-assigned network resources.
Accordingly, what are needed are methods and apparatus for expeditiously releasing network resources for a mobile station to overcome the deficiencies in the prior art.